Method for prepress-time color match verification and correction

ABSTRACT

A method of matching color elements for objects within a print job prior to printing, includes for each page in the print job, identifying all objects and their associated object properties within the page; for each object, identifying, according to predetermined object property criteria, if the object is a candidate for a color matching task; for each of the identified candidates, filtering the object properties using a predetermined visual relevance metric, such that objects having less than the predetermined visual relevance metric are removed from consideration; defining each candidate object satisfying the predetermined visual relevance metric as a color matching object with respect to at least a second color matching object thus defining a color matching object group; for each such color matching object group, either alerting a user to a problem or resolving the problem by assigning common rendering across the color matching object group.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from provisional Application Number60/697,650 filed Jul. 8, 2005, the contents of which are incorporatedherein by reference. This application is related to co-pending,co-assigned U.S. patent application Ser. No. 11/178,129 filed Jul. 8,2005 to Thomas C. Rich et al. for “Method for Prepress-time Color MatchVerification and Correction, application Ser. No. 11/178,106 filed Jul.8, 2005 to David E. Rumph et al. for “Method for Prepress-time ColorMatch Verification and Correction”, and application Ser. No. 11/178,017filed Jul. 8, 2005 to Patrick Harrington et al. for “Method for RemoteProofing of DFE Color Architecture”, the contents of all of theforegoing are incorporated herein by reference.

BACKGROUND

This disclosure relates to methods for pre-press color matchverification and correction, with special emphasis on limiting the userinvolvement in said process by incorporating an intelligentpre-filtering to judge color match relevance. Color management providesthe tools to reconcile the different color capabilities of monitors,scanners, printers and printing presses to ensure consistent colorthroughout the production process. Color management also allows digitalproofing, which is especially important now that the average run-lengthof print jobs is continuously declining. Color management is based ondefined and standardized color spaces. The range of colors, or gamut,that can be captured on film, displayed on a computer monitor, orrendered by a printer vary significantly. Additionally, the range ofcolors that can normally be perceived by the human eye in generalexceeds the colors that can be presented by the different devices.

The different attributes of the different color devices also have led todifferent mathematical descriptions of the individual color spaces, withtwo major color space classes being additive and subtractive colorspaces. RGB is an additive color space that combines red, green and bluelight to create all other colors. RGB color spaces are used by monitors,digital camera and scanners. CMY and CMYK color spaces as are used inmost printing processes, on the other hand, and are subtractive colorspaces using cyan, magenta, yellow and optionally black inks on paper toabsorb red, green and blue light. The remaining reflected light is thecolor perceived by the viewer.

When transferring color descriptions from one device to another, ICC(International Color Consortium) profiles are frequently used. An ICCprofile is a computer file that describes the mathematicaltransformation of one color space to another. For efficiency reasons,this is generally done through an intermediate connection space (named aProfile Connection Space PCS), resulting in ICC profiles for inputdevices giving the mathematical description of the input device color tothe connection space and ICC profiles for output devices giving themathematical description of the connection space to the output device. Acolor engine (also called a color matching module or CMM), reads the ICCprofiles and converts the colors between the different devices. Multipleinput descriptions, when converted to a single output device, can resultin the identical color, i.e., one color might be described in amultitude of mathematically different color spaces on the input side.After correct mapping to the single output color space these differentcolor descriptions will again describe the same color, as seen by ahuman.

Most electronic documents to be printed or output on a particular deviceinclude multiple elements, such as text, photos, graphics and the like.Many electronic documents are also a composite of other smallerdocuments and elements. For example, photos may be pasted into a largelytext document at different locations. Color graphics and monochromeimages may occur on the same page. The individual elements of anelectronic document that are intended to match in color may berepresented in a variety of color spaces, a situation which for examplemay arise because those elements are derived from prior documents ofdiffering origins. This situation may not be immediately apparent to theuser, because the colors of the objects appear to match on the displayor when printed using a straightforward color transformation process,such as is typical in ICC-based color management.

One problem arises when more sophisticated object optimized colortransformation is involved, such that different source color definitionstake different color transformation paths. For example, two differentobjects of identical color—potentially described in different forms anddifferent color spaces—might be transformed by the CMM to optimally usethe device capability, incorporating typical device compromises as thewell known compromise between color and detail preservation, or the wellknown compromise between color precision and color representationtexture. Additionally, if one object's color is specified in sRGB forinstance, and another object's color specified in SWOP CMYK(Specifications for Web Offset Publications CMYK), the color processingneeded to produce the device CMYK for the specific marking process mayproduce a different device CMYK quadruplet for the two objects. This canbe understood because all 3-to-4 transformations, such as the one fromsRGB to CMYK, are underdetermined and additional degrees of freedom canbe incorporated. Examples are differing black generation/blackpreservation strategies, even if the two objects would have matchedexactly on a SWOP press using the standard SWOP assumptions.

Another problem arises when more sophisticated color transformation isinvolved, such that non-color differences in the source (e.g., differingobject type) that cause the objects to take different colortransformation paths. One instance of this is that the Xerox CorporationDocuSP color DFE (digital front end) can assign different ICC renderingintents to different object types. For example, by default text isassigned a “Saturation” rendering intent, while graphics are assigned a“Relative Colorimetric” rendering intent. Especially for colors near theedge or outside the printer's color gamut, the processing of the sourcecolor may produce visibly different results. This type of processing iscommonly referred to as Object Optimized Rendering (OOR) and is intendedto optimally utilize the machine capabilities and trade-offs. Consider,for example, a print job consisting of three characters printed in afirst color on a white background adjacent to three characters printedin white on a background of the first color. Using a program such asAdobe Acrobat, the first color would be displayed on a monitor for auser to view. When the job is printed using the DocuSP's colorprocessing, the first color is slightly different.

These situations are difficult to find prior to printing without a verydetailed and precise understanding of the DFE's color processing, whichthe typical user does not have. Consequently, color matching differencesof these types have typically been discovered only upon printing, whenresolution is costly and time-consuming. What is needed is a methodwhich alerts a user to color mismatch problems prior to printing andallows the user to correct any mismatches. In some cases it may beappropriate to change the “problem” criteria described above to betterreflect human perceived relevance thereby reducing the number of objectsexamined and to add additional relevance criteria that are based onother object properties than the described and measured colorproperties. Also, what is needed is a way to prioritize the visualimportance of the color mismatches along with a resolution approach thatcan resolve the different cases in the respectively appropriate manner.

Proofing is a convenient means of providing a user, especially a remoteuser of a preview of how a particular print job will appear when printedon the selected printer. Currently, there are no color transformationutilities that mimic a DFE's color architecture remotely, i.e.,independently of the production rip. Proofing color transforms aretypically performed via an output ICC profile for a target printer usedas a CMYK source profile on the DFE driving a proofer. Unfortunately,the target ICC profile can only characterize one print condition forCMYK image objects, and fails to correctly model any sophistication inthe color processing of the target printer beyond the simple ICCworkflow. What is needed is a remote proofing method for displaying aproof of a print job that reflects the remote printer's architecture.

SUMMARY

Disclosed in embodiments herein is a method of color match verification,which may be implemented as a software tool operating on a computer ormicroprocessor, applied prior to printing, that identifies color matchproblems arising from different color processing for different sourcecolor representations, filters the problems by visual relevance andprovides a way to either automatically correct these color matchproblems, or in the alternative, provides a way for a user to correctthem with minimal interaction. The method accomplishes this by acombination of generating color mismatch metrics, along with a visualrelevance metric based on additional properties, such as object type,object size, object proximity, or the like. These two criteria might begenerated sequentially or in parallel, depending on the more efficientimplementation on a specific device. For the purpose of simplicity ofdescription we will use a logical order of first generating the purecolor mismatch metric, followed by the additional object-based metric.

Disclosed in other embodiments herein is a method of color matchverification, which may be implemented as a software tool operating on acomputer or microprocessor, applied prior to printing that identifiescolor match problems arising from different color processing fordifferent source color representations and provides a way to eitherautomatically correct these color match problems, or in the alternative,provides a way for a user to correct them. The method accomplishes thisby transforming each object's source color using a prototypical colortransformation, identifying sets of objects having colors that matchusing the prototypical process, and then reconverting the source colorsusing the actual color transformation processing of the selected outputdevice, and ensuring that the objects' colors still match. If they donot, in one embodiment, color matching may be performed automaticallyusing a predetermined criterion. Alternatively, the mismatching colorsmay be displayed in a user interface that can be used to enable a userto manually update the source color definitions of the various objectsso that they are specified in the same way, and therefore will matchwhen printed.

A computer-implemented method of matching color elements for objectshaving different source color definitions within a print job prior toprinting, according to one embodiment includes identifying all sourcecolors to be printed within the print job and object type associatedwith each instance of a source color; identifying any source colorshaving at least two different source color definitions; for each sourcecolor having at least two different source color definitions, selectingone of the source color definitions in accordance with a predeterminedcriterion; and assigning the selected source color definition to atleast one other instance of the source color for that object type. Thepredetermined criterion may include the following relationship: for eachsource color having at least two different source color definitions forthe same object type, assigning the selected source color definition toall other instances of the source color for that object type.Alternatively, in the method, selecting one of the source colordefinitions may be accomplished by displaying the source colors havingat least two different source color definitions and associated objecttypes in a user interface; and responsive to input from a user,assigning a user-selected source color definition to all user-selectedinstances of the user-selected source color. Identifying any sourcecolors having at least two different source color definitions may beaccomplished by: for each object in the print job, transforming eachobject of the same object type using a prototypical colortransformation; identifying sets of objects having source colors thatmatch within a first tolerance level after the prototypicaltransformation process; for each set of objects having source colorsthat match, transforming each matching object's original source colorsusing a target printer's color space; and identifying any of thetransformed colors of the matching objects within the set that do notmatch within a second tolerance level. The prototypical colortransformation comprises an ICC-based profile.

A computer-implemented method of matching color elements for objectshaving different source color definitions within a print job prior toprinting, in accordance with another embodiment, includes convertingeach object's source colors to a common color space; identifying groupsof objects having source colors in the common color space that matchwithin a first tolerance level; within each group of objects havingmatching source colors: transforming each object's original source colorinto a target printer's color space using the target printer's colortransformation path; identifying any of the transformed colors of thematching objects within the group that do not match within a secondtolerance level; if at least one of the transformed colors does notmatch the other transformed colors in the group, correcting mismatcheswithin the group.

The method may further include displaying any groups of mismatchedobjects within a user interface; and responsive to user input for eachgroup of mismatched objects displayed in the user interface, assigning auser-selected source color definition of the user-selected transformedcolor to all objects within the group. The method may also includemodifying the target printer's color transformation path according toany relevant printer settings and print job parameters. In the method,converting each object's source colors to a common color space may beaccomplished by converting each object's source color into a profileconnection space (PCS) representation using a source ICC profile.Transforming each object's original source color into a target printer'scolor space using the target printer's color transformation path may beaccomplished by converting the PCS representation to the common colorspace using an output profile. Correcting mismatches within the groupmay be accomplished by an algorithm (or by user input) which examinesthe objects within the group; determines if the objects in the group areintended to match one another in accordance with a predeterminedcriterion; and if not, removes those objects not intended to match fromthe group. Examining the objects within the group may be accomplished,for each object in the group, by examining that object's source colors,colors as expressed in the common color space and colors as expressed inthe target printer's color space. The predetermined criterion used bythe algorithm may be determining which objects in the group of are ofthe same object type. The method may be performed on a completedocument, or alternatively, on a page-by-page basis.

In some cases two objects may have the same source color space and samecolor value, but transform into colors in the target printer spacebecause of different rendering intents (which control, for example, theformulation of CMY vs. K and the mapping of out-of-gamut colors into theprintable gamut). In the case of DocuSP, the job or queue settings cancause different object types to be color converted using differentrendering intents. This yields a possibly unexpected mismatch eventhough the document creator assigned two objects, say color text and abar of a bar chart, the same source color. In some cases, even when adocument is “fixed” by making all the source colors the same (as in theforegoing method), this does not fix the color mismatch when the job isprinted using settings that assign different rendering intents todifferent object types. For example if the source colors were in factalready the same and the object type cannot be changed readily, theproblem can be fixed by changing the chosen printer settings. In thiscase the method either: warns the users of the unfixable condition andinstructs the user to change the printer settings, or in thealternative, automatically changes the printer's job settings inaccordance with some predetermined criterion.

Disclosed in another embodiment herein is a method of color matchverification, which may be implemented as a software tool operating on acomputer or microprocessor, applied prior to printing that identifiescolor match problems arising from different color processing to beperformed in the DFE/printer. The method in this embodiment accomplishesthis by transforming each object's source color using a prototypicalcolor transformation, identifying sets of objects whose colors matchusing the prototypical process, and then reconverting the source colorsusing the actual color transformation processing of the selectedDFE/printer, and ensuring that the objects' colors still match. If theydo not, they are included in a list on the user's display, includinginformation that indicates why the items will not match when printed.

A computer-implemented method of identifying color mismatches forobjects having different rendering intents within a print job prior toprinting, may include identifying all objects within the print job, eachobject's type, each object's rendering intent and all source colorsassociated with each object; for each object in the print job,transforming each object's source colors using a prototypical colortransformation; identifying sets of transformed objects having sourcecolors that match within a first tolerance level after the prototypicaltransformation process; transforming all transformed objects using atarget printer's color space; identifying any of the transformed objectsin each set that do not match within a second tolerance level to form agroup of mismatched objects; and displaying the group of mismatchedobjects in a user interface, wherein the display includes each object inthe second set, all source colors and rendering intents associated witheach object and information indicating which objects will not match whenprinted on the target printer.

A computer-implemented method of matching color elements for objectshaving different rendering intents within a print job prior to printing,may include identifying all objects within the print job, each object'stype, each object's rendering intent and all source colors associatedwith each object; for each object in the print job, transforming eachobject's source colors using a prototypical color transformation;identifying sets of transformed objects having source colors that matchwithin a first tolerance level after the prototypical transformationprocess; transforming all transformed objects using a target printer'scolor space; identifying any of the transformed objects in each set thatdo not match within a second tolerance level to form a group ofmismatched objects; identifying any object types within the group ofmismatched objects having at least two different rendering intents; foreach object type having at least two different rendering intents,selecting one of the rendering intents in accordance with apredetermined criterion; and assigning the selected rendering intent toat least one other instance of that object type.

Some print jobs may be so complex that color mismatches may occur formultiple reasons. The foregoing methods can be combined. The method ofmatching color elements for objects having different source colordefinitions can be performed and selected source color definitionsassigned to mismatching source colors for the same object type. Onceobjects of the same type have the same source color definitions, themethod of identifying color mismatches for objects having differentrendering intents can be applied. Objects with the same source color butdifferent rendering intents can be identified and then either correctedautomatically or displayed in a user interface for a user to correct.

Disclosed in other embodiments herein is a method for remote proofing adigital press by performing the color rendering of a specific DFE andprinter, including taking into account job and printer settings, whilemaintaining vector objects. In one exemplary embodiment, this methodcolor renders a file to a PDF/X-1a format to enable a portableproof-ready file, independent of the target print system. The PDF/X-1a'soutput intent tag identifies the intended print condition within thefile. Adobe Acrobat can use this tag to convert colors from the printcondition to the monitor space for soft proofing. Additionally, therendered PDF/X-1a file can be sent to any device that supports the PDF/Xstandard and automatically convert colors from the output intent colorspace to the proofer color space for an accurate hard copy proof. Thisfunctionality automates and streamlines the proofing task of the enduser because there is no need to find and load the correct ICC profileon the proofing system.

A method of proofing a print job to be printed on a remote printer, mayinclude providing an input print job comprising a plurality of objectsand remote printer settings; identifying all objects within the printjob, each object's type, each object's rendering intents and all sourcecolors associated with each object; for each object in the input file,transforming each object's source colors using the remote printer'scolor space; creating an output proof print job comprising thetranslated objects and an ICC profile corresponding to the remoteprinter; and outputting the output proof print job on a proofing device.The input print job may be formatted as a PDF file. The output print jobmay be output on a monitor or other printer. The color match methodsdescribed above may be applied during the transforming steps.

A method of proofing a print job to be printed on a remote printer, mayinclude providing an input print job comprising a plurality of objectsand remote printer settings; identifying all objects within the printjob, each object's type, each object's rendering intents and all sourcecolors associated with each object; for each object in the input printjob, transforming the object's color to the target printer's colorspace, using the target printer's actual color conversion process,taking into account printer settings, job ticket, and media to produce adocument having colors that are represented in the target printer'sdevice CMYK color space; converting the document to PDF/X-1a format,including tagging the document with an output profile corresponding tothe target printer; sending the resulting PDF/X-1a file to a PDF/X-1acompliant output device.

In the foregoing method for matching color elements for objects havingdifferent source color definitions and method for matching colorelements for objects having different rendering intents, matching isdone by computing color distance and clustering. This may beaccomplished by calculating the difference between color objects in adocument, where the difference is defined by rendering the objectsthrough a “standard” SWOP path and contrasting that data with therendering through an Object Optimized Rendering (OOR) path. Thesemethods generate a large amount of data in both the automatic mode andfor the user interaction mode. In some instances, it may be useful tofilter the data generated using the foregoing methods. It may be usefulto redefine the color match problem used in the foregoing method inorder to reduce the number of returned mismatched objects. It may alsobe useful in the user interaction embodiment to provide additionalrelevance criteria that are based on other object properties than thedescribed and measured color properties.

In the foregoing method for matching color elements for objects havingdifferent source color definitions and method for matching colorelements for objects having different rendering intents, matching isdone by computing color distance and clustering. This may beaccomplished by calculating the difference between color objects in adocument, where the difference is defined by rendering the objectsthrough a “standard” SWOP path and contrasting that data with therendering through an Object Optimized Rendering (OOR) path. Thesemethods generate a large amount of data in both the automatic mode andfor the user interaction mode. There is a possibility that in thismethod in an automatic mode, too many objects may be rendered in asub-optimal way (with no OOR) and that in the user interactive mode, toomany potential problems may be displayed to the user, resulting inexcessive labor cost or user frustration. It is thus highly desired tofilter the data generated using the foregoing methods. It may be usefulto redefine the color match problem used in the foregoing method inorder to reduce the number of returned mismatched objects. It may alsobe useful in the user interaction embodiment to provide additionalrelevance criteria that are based on other object properties than thedescribed and measured color properties.

Disclosed herein in yet other embodiments is a computer-implementedmethod of matching color elements for objects having different sourcecolor definitions within a print job prior to printing, including: foreach page in the print job, identifying all objects within the page,each object's type, each object's color space, each object's renderingintent and all source colors associated with each object; identifying,according to a predetermined problem criterion, any potential problemobjects within the page possibly requiring color matching; for eachpotential problem object, identifying any source colors having at leasttwo different source color definitions; for each source color having atleast two different source color definitions that would match or verynearly match. For the actual problem objects, an automated correctioncan be chosen, for example by using standard SWOP assumptions for theproblem objects and by using standard OOR assumptions for all otherobjects. A user-interactive system needs only to alert the user to theactual problem objects, allowing the user to select the appropriaterendering. At this point, it should be understood that the actualdefinition of the problem objects includes user or job settings withrespect to color difference in say Lab ΔE, with respect to object types,object sizes and the like.

Disclosed herein in yet other embodiment is a computer-implementedmethod of matching color elements for objects within a print job priorto printing, comprising: for each page in the print job, identifying allobjects and their associated object properties within the page; for eachobject, identifying, according to predetermined object propertycriteria, if the object is a candidate for a color matching task; foreach of the identified candidates, filtering the object properties usinga predetermined visual relevance metric, such that objects having lessthan the predetermined visual relevance metric are removed fromconsideration; defining each candidate object satisfying thepredetermined visual relevance metric as a color matching object withrespect to at least a second color matching object thus defining a colormatching object group; for each such color matching object group, eitheralerting the user to a problem or automatically resolving the problem byassigning common rendering across the color matching object group. Theobject properties may include at least two of color attributes, objectattributes, object location attributes and object size attributes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a user interface displaying groups of colormismatches.

FIG. 2 illustrates a user interface displaying groups of colormismatches with one item deselected.

FIG. 3 illustrates a user interface displaying results after analysis ofmismatches based on rendering intents.

FIG. 4 illustrates another user interface displaying an additionalwindow for editing source color definition.

FIG. 5 illustrates a large fill area adjacent to small object.

FIG. 6 illustrates non-touch objects having a stroke or outline.

DETAILED DESCRIPTION

Various methods will be described for ensuring that the individualelements of a document to be printed that match in color will match inthe printed document. In the following description, these methods willbe described as implemented in software tools operating on a computersystem, which sends print jobs to an output or target printer. Some ofthese tools can be configured to automatically make mismatching colorsmatch in accordance with some predetermined criterion. Others of themethods will provide the mismatching colors in a user interface for theuser to select which, if any, colors to match. Indeed, even in the userinterface implementation, some users may elect to have the methodautomatically match colors.

A first method can be used to correct for color mismatch problemsarising from different color processing for different source colorrepresentations. In this method, colors of objects in the document areanalyzed for mismatches, then corrected. For each object in the document(excluding sampled images), the object's colors are converted to acommon color space using a simple, ICC-based approach. That is, thesource color is converted into a profile connection space (PCS) using asource ICC profile, and then the PCS representation is converted to thecommon color space using an output profile, e.g., a printer profile.Objects in the document may be then clustered into groups or sets thathave matching colors in the common space. Matching is determinedaccording to some first tolerance range by comparing the color valuesgenerated as a result of the transformation for the particular objects.If the numeric values are within the first tolerance range, the colorsare deemed to match.

In one embodiment, matching is done by computing color distance andclustering. Color distance is computed as Euclidean distance (squareroot of the sum of squares of the component differences) in the commoncolor space. An alternative would be to further convert the color fromthe common space to a visually uniform space such as CIE L*a*b*, andthen compute Euclidean distances in the visually uniform space. Distanceis computed between cluster centroids. A cluster's centroid is theaverage of the member objects' components, with each object weightedequally. An alternative would be to weight each object by an attributesuch as area of ink coverage. Clustering is done as follows: Initiallyeach object is the sole member of a cluster. For every cluster thedistance to its nearest neighbor is computed. Repetitively the twonearest clusters are merged into one, the new cluster's centroiddetermined, and all affected nearest neighbor distances updated.Repetition terminates when the nearest cluster distance exceeds aspecified threshold. The clustering does not involve interaction withthe user.

Within each group, each object's original source color is transformedinto the target printer's color space using the actual colortransformation path of the DFE for that printer, taking into account anyrelevant printer settings and job ticket parameters. If the colors ofthe objects within a group, as expressed in the target DFE/printer'scolor space, do not all match within a second tolerance range (i.e.,their output color values after the second transformation are not withinthe second tolerance range), the method will either correct the mismatchautomatically using a predetermined criterion or display all of thoseobjects in a list of mismatches in a user interface for the user tocorrect manually. The method can be applied to the entire document or ona page-by-page basis.

One example of a predetermined criterion for matching mismatching colorsis for each source color having at least two different source colordefinitions for the same object type, assigning a selected source colordefinition to all other instances of the source color for that objecttype. This criterion ensures that all objects of a particular type willhave the same source color definition and be processed the same.

Not all users will want to have source color definitions set by defaultfor all objects of a particular type. In this case, the method willdisplay mismatches in a user interface. FIG. 1 illustrates a userinterface which shows various groups of objects that have been analyzedusing this method. A document on the left shows a series of six groupsof source colors, each having four instances. Results of analysisaccording to the method are displayed on right, showing four groups ofcolor mismatches. Each line describing each mismatched object includes arepresentation of the object's color as expressed in the target space,the page in the document on which the object was found, the object type,source color, common color (SWOP CMYK in this case) and target color(DocuSP CMYK in this case). Note that in FIG. 1, each object's color hasa different color value.

For each mismatch group, the user examines the objects listed, includingtheir source colors, colors as expressed in the common color space, andcolors as expressed in the DFE/printer's native color space, anddetermines if the objects in the group were intended to match eachother. Objects that were not intended to match are deselected. The userthen selects one of the objects in the group whose source colorrepresentation is what all of the objects in the group should have been,and clicks a “unify” button. The tool writes the source color of theselected object into the color property for all of the objects.(Alternatively, some other source color chosen by another means may beused for the unification process.)

FIG. 2 shows a group of objects with one member deselected, and onemember highlighted as the exemplar for unification. Color group withDeviceCMYK object deselected (second from bottom in list; note uncheckedcheckbox) and PANTONE object highlighted for unify. The highlightedobject is also indicated by a dashed line in the document view at left.When the user clicks the “Unify” button the three checked-marked limegreen objects will all have their color definitions changed to the samePANTONE color as the highlighted object.

A software tool implementing the above-described method was implementedin a plug-in which may be installed in Adobe Acrobat. The followingillustrates the installation and operation of this tool. Operation:Correct installation of the tool results in a new “XeroxTools” menuappearing on the main menu bar in Acrobat. Two tools are provided:ColorMatch and Remote Proof. Although either of the plug-in tools may beopened before opening any document, a document must be opened in Acrobatbefore either of these tools may be run.

Color Match. The purpose of the Color Match tool is to help a user findand fix problems with color matching within a document. It goes througha two-step process analyzing the user's document. If the user hasinstalled the printer data files at the default location, then the toolwill open immediately. Otherwise, the user will be prompted to locatethe DocuSP directory on the disk, which contains the printer data files.

Finding problems. In the first step, all objects in a document aretranslated into Acrobat's Working CMYK space (e.g., SWOP Coated), andgrouped into sets of objects that match within the specified variance.In the second step, all of the objects in each matching group aretranslated into DocuSP CMYK using the printer and queue settingsselected by the user. Objects that matched in the first step (i.e., inthe default CMYK space), but do not match in the second step (i.e., inthe DocuSP color) are shown in the tool. For each object, the objecttype, source color (both stroke and fill), and corresponding standardand DocuSP CMYK colors are shown in a mismatch list in the large box inthe center of the plug-in tool. When the user selects the list entry,the corresponding object in the document is centered in the documentwindow, and the object is highlighted in the manner selected by the“highlight” menu (one of Outline, Invert or Flash). This makes it easyto determine which object the tool has flagged.

Example of Clustering Algorithm. Consider a test file which consists of4×4-bluegrey-0+4+8+12.pdf with variances 16, 18, 20, 40 in a PDF formatdocument. The PDF document content is enumerated by the facilities ofthe Adobe PDF Library package. The items under examination are instancesof the abstract superclass PDEElement, which encompasses many types ofobject including PDEPath, PDEText and PDEShading, the only types ofinterest to ColorMatch, as well as many others such as PDEImage andPDEXObject, which are ignored.

In each instance of PDEPath encountered, as many as two color values arepossible, the stroke color and the fill color. Each instance of PDETextmay contain one or more text runs; each text run may specify a strokecolor value and/or a fill color value. Each PDEShading is treated asspecifying two color values, if it is an Axial or Radial shading, orfour color values, if it is a Function-Based shading; the other types ofshading are not supported. Each non-null color value is added toColorMatch's data base of document color values.

A color value, called a PDEColor Spec by Adobe, consists of a colorspace and its requisite tint values. In Adobe Acrobat's formulationthere are eleven color spaces: three device spaces DeviceGray, DeviceRGBand DeviceCMYK; four CIE-Based spaces CalGray, CalRGB, Lab and ICCBased;and four special color spaces Pattern, Indexed, Separation and DeviceN.The device spaces are simple uncalibrated spaces of one, three and fourcomponents respectively. The calibrated CIE-Based spaces CalGray, CalRGBand Lab consist of one, three and three components respectively; anICCBased space may require one, three or four component values. ASeparation space is a spot colorant and a tint, or amount of colorant; aDeviceN space is a blend of one or more spot colorants and their tints.An Indexed color space uses a small integer component value to index atable of arbitrary color values specified in another color space. APattern space is either a Tiling, which replicates a fixed bounded imageover a grid, or a Shading, which sweeps a varying color value across aregion of the document; Pattern space values do not fit the model (space& component values) applicable to other color spaces. ColorMatchcurrently supports all possible cases except Tiling Pattern spaces andthe four Mesh Type Shading Pattern spaces.

ColorMatch's data base of document color values is organized as acollection of sets of objects. Each set, called a Color SpecSet, isdistinguished by a specific PDEColor Spec and a specific renderingintent, which can be either Graphic, used for paths and shadings, orText. The objects in a particular set are instances of PDEElement whichshare the set's distinguishing PDEColor Spec and intent. Usually eachColor SpecSet will have unique distinguishing values and contain allelements matching those values, but, if the PDF document is notstructured optimally, it is possible for two or more sets to haveidentical distinguishing values, in which case the sets will bedisjoint, that is each object will be a member of one set only. Mostfurther processing is focused upon the Color SpecSets acting as proxyfor the contained elements.

The next step of the analysis begins with the transformation of eachColor SpecSet's color value to Acrobat's CMYK Working Space, which isspecified in Acrobat's Color Management Preferences dialog and whichdefaults to “U.S. Web Coated (SWOP) v2”. Hereafter in this document thattransformed value will be referred to as the SWOP value although theactual Working Space might be another CMYK space. Then the database isfurther organized into a collection of sets of Color SpecSets. Each set,called a SWOPcolor Set, is distinguished by a unique SWOP value and, atthis stage of the analysis; each set contains all Color SpecSets exactlymatching its SWOP value, and no others.

Next, if the user has specified a nonzero SWOP Variance, SWOPcolor Setswith sufficiently similar SWOP values are merged. Initially eachSWOPcolor Set contains Color SpecSets with one identical SWOP value. Theclustering algorithm iteratively merges the nearest two SWOPcolor Sets.The separation between SWOPcolor Sets is a simple Euclidean distance inCMYK space. The location of each SWOPcolor Set is its centroid, aweighted average of the individual Color SpecSet SWOP values, weightedby the number of PDF elements in each Color SpecSet. (A more ambitiouscalculation might weight elements by a more complex criteria such asamount of ink coverage.) The clustering algorithm terminates when thenearest two SWOPcolor Sets are more distant than the user-specified SWOPVariance.

Upon completion of this clustering process, each SWOPcolor Set isdistinguished by a SWOP value at the centroid of the set's members, andeach set contains all Color SpecSets whose SWOP values fall within aspherical region of radius specified by the SWOP Variance and centeredat the centroid.

Fixing Problems. The ColorMatch plug-in provides a way to alter the PDFfile so that all objects within a color group have the same sourcecolor. This feature is called unify. To use Unify, the user selects oneof the objects in a color group, and clicks the Unify button at thebottom of the tool. The source color from the selected object becomesthe source color for all the checked objects in that group. Since theobjects now match in color, they are removed from the mismatch list. Ifthe user does not want the new source color to be applied to certain ofthe objects in the set, simply uncheck the checkbox at the left end ofthe list entry for that object. The PDF document will be updated whenthe user clicks the tool's “Unify” button. Even after the user has“Closed” the tool, the altered document has not been saved back to thedisk. The user can save the document, overwriting the original sourcecolors, or the user can “Save As” to a new name, if the user wishes topreserve the original document.

Color Editor. If none of the original objects has the desired color,this version of ColorMatch now supplies a color editor. Select theobject whose color is to be modified and click the “Edit” button beneaththe list of objects. A color editor will appear, which allows the userto modify the components of the source color (or select from a list ofspot colors known to the selected target printer, in the case of asource spot color) as shown in FIG. 4. The user can also convert thesource color to either SWOP CMYK or the target printer's CMYK. The usercan also revert to the source color by selecting “Original” from thecolor space drop-down menu. Clicking “OK” updates the color of the“inkwell” on the main ColorMatch window. The user can now select anyobject and click “Paste” to update that object's color. If the usermerely wants to copy the color of an object from one group into anothergroup, the “Copy” button beneath the object list will copy the color ofthe selected object into the “inkwell” without opening the color editor.

Remote Proofing. The Remote Proofing tool color converts the text andgraphic objects in a PDF document to DocuSP CMYK and produces a PDF/X-1afile with an embedded printer-specific ICC profile. The ICC profilescurrently embedded are for the iGen3, DC 2060, or DC 6060 printers.There is currently only one ICC profile per IOT available. To produce aremote proof PDF document: Choose Xerox Tools>Remote Proof. Select aPrinter. Select a Queue. Click the Create Proof button. A new PDF/X-1adocument will be created. “x1a” will be appended to the new document'sfile name. The file can then be sent to a PDF/X-1a compliant proofprinter. Note: If the document has security features enabled, the RemoteProof tool will prompt for a password before it can produce the proofdocument. The new proof document will not inherit the security featuresof the original.

Note: If the fonts in the original document are not embedded or if theoriginal document has actions, transparency, or separated pages, thefile that will be produced will not be PDF/X-1a compliant. The toolcurrently detects these cases and alerts the user. Other requirementsfor PDF/X-1a compliance that the tool does not currently check for are:No LZW compression; Page boxes must be nested properly; Halftone must beType1 or Type5; No Halftone Name key; No HTP key within an ExtGStateresource; No embedded PostScript; Alternate image not default forprinting; Annotation and Acrobat form elements must be outside ofTrimbox and Bleedbox; No Javascript; No operators not defined in PDF1.3; No File Specifications—typically used for OPI comments as well asexternal streams; and No OPI in Form Xobject or Image Object.

A second method can be used to correct for color mismatch problemsarising from non-color differences in the source (e.g., differing objecttype) causing objects to take different color transformation paths. Oneexample of is when the DocuSP color DFE assigns different ICC renderingintents to different object types. In the method, for each object in thedocument (excluding sampled images), the object's colors are convertedto a common color space using a simple, ICC-based approach. That is,each source color is converted into a profile connection space (PCS)using a source ICC profile, and then the PCS representation is convertedto the common color space using an output profile, e.g., a printerprofile. All objects are then clustered into groups or sets havingcolors that match in the common space to within some tolerance range.Within each group or set, each object's original source color is thentransformed into the target printer's color space using the actual colortransformation path of the DFE for that printer, taking into account allrelevant printer settings and job ticket parameters. If the colors ofthe objects within a group, as expressed in the target DFE/printer'scolor space, do not all match within a second tolerance range, displayall of those objects in a list of mismatches. Color matching isdetermined by comparing output color values generated by the particulartransformation. Alternatively, the first transformation may beeliminated and clustering can be performed independently in eachrepresented color space.

FIG. 3 illustrates a user interface that shows various groups of objectsthat have been analyzed as described. Document to be analyzed is shownat left. Results of analysis on right, showing one group of colormismatches, consisting of two objects. The line describing eachmismatched object includes a representation of the object's color asexpressed in the target space, page on which the object was found, theobject type, source color, common color (SWOP CMYK in this case) andtarget color (DocuSP CMYK in this case). A line of warning text beneaththe line for each object shows in red the reason for the mismatch, inthis case a difference in rendering intent. Note that in FIG. 3, eachobject has the same color value.

For each mismatch group, the user examines the objects listed, includingany warnings, and determines if the objects in the group were intendedto match each other. The user then corrects the problem causing themismatch, e.g., by changing the printing settings (the DocuSP queue inthis example). As workflow systems become more tightly integrated, e.g.,with JDF, the tool may provide a means to directly change the printersettings via the job ticket.

Remote proofing enables a user to view locally a print job that will besubmitted to a remote printer, such as a production printer like XeroxCorporation's iGen3, DocuSP, DC 2060 and DC 6060. This is similar to theprocess used by photographers: a proof set of photographs is sent to acustomer for selection before printing the photographs in final formusing the best quality paper and processes. A method for remote proofinga digital press performs the color rendering of a specific DFE andprinter, taking into account job and printer settings, while maintainingvector objects. In one exemplary embodiment, this method color renders afile to a PDF/X-1a format to enable a portable proof-ready file,independent of the target print system. The PDF/X-1a's output intent tagidentifies the intended print condition within the file. Adobe Acrobatcan use this tag to convert colors from the print condition to themonitor space for soft proofing. Additionally, the rendered PDF/X-1afile can be sent to any device that supports the PDF/X standard andautomatically convert colors from the output intent color space to theproofer color space for an accurate hard copy proof. This functionalityautomates and streamlines the proofing task of the end user becausethere is no need to find and load the correct ICC profile on theproofing system.

PDF/X-1a is a new file format, intended for the reliable exchange ofgraphic arts data. PDF/X-1a offers additional security for files thatare submitted remotely. Fonts and images must be embedded, eliminatingthe possibility of font substitution or missing elements. Color must beCMYK. Mechanical specifications (media, trim etc.), trapping and printconditions (such as SWOP) must be defined, so there is far less marginfor error. The PDF/X-1a standard addresses blind exchanges where allfiles should be delivered in CMYK (and/or spot colors), with no RGB ordevice independent (color-managed) data. This is a common requirement inmany areas around the world and in many print sectors—usually tied to anenvironment where the file supplier wants to retain maximum control ofthe print job. It's very hard to transmit data as RGB or Lab and stillto include custom trap definitions, for instance. The first PDF/X-1astandard, better referred to as PDF/X-1a:2001 is published as ISOstandard 15930-1:2001.

For each object in the document, convert the object's color to thetarget DFE/printer's color space, using the actual DFE/printer's actualcolor conversion process, taking into account printer settings, jobticket, and media. This conversion produces a document whose colors areall represented in the target printer's device CMYK color space. Convertthe document to PDF/X-1a, which includes tagging the file with theoutput profile corresponding to the target printer. Send the resultingPDF/X-1a file to a PDF/X-1a compliant soft proofing system or hardproofing device.

Structurally, “RemoteProof” may be implemented as a separate tool, butsharing many of the same software components as the “ColorMatch” Acrobatplug-in described above. In particular, the color conversion extractedfrom the DocuSP DFE is used heavily by both RemoteProof and ColorMatch.Likewise, the same code may be used to access each object in the PDFfile, although what is done with each object differs between the twotools.

Functionally, a user would interact with RemoteProof as follows. In themethod of remote proofing, an input PDF file is opened. The file ischecked for compatibility with the PDF/X-1a standard, and warnings fornon-compliant features are generated. For each object in the file: thesource color is translated to the specified device output color spaceusing the full sophistication of the DFE's color conversion. Thisconversion may include automatic selection of different renderingintents based on object type, custom spot color dictionaries (e.g., forbest Pantone compliance), etc. The object that has been color-translatedis reinserted into the PDF file in place of the original object. Forobjects of compound color, for example smooth shading and sampledimages, each source color involved in specifying or defining thecompound color is translated. An ICC profile corresponding to thetargeted output color space is attached to the PDF file. The file ismarked as a PDF/X-1a file, unless there are compliance issues.RemoteProof may be implemented as an element of an automated workflow,although an Acrobat Plug-in version implemented is invoked manually by auser.

A purpose of Remote Proofing is to enable proofing of the effects of thefull DFE conversion on a proofing device (either monitor or proofprinter) other than the targeted printer. For example, a graphicaldesign house may be targeting a document to an iGen3, but the designhouse does not have one at their design house so they outsource theprinting to a commercial printer who has the iGen3. How do the designerssee what the output is going to look like? RemoteProof can be used toconvert the document to iGen3 CMYK, and use an ICC “device link” profileof a CMYK proof printer, along with the profile specifying iGen3 CMYKthat RemoteProof embedded in the PDF/X-1a file it generated, to producea proof print that mimics the iGen3, including the DocuSP colorconversion, to the limits of the proof printer's gamut.

Referring again to FIG. 1, there is shown a typical information screenfor a method of color matching based on different source colordefinition. In essence, all document objects are listed and thecorresponding color values are given in various color spaces. Thismethod is essential to a color expert who wants to assure thateverything in the document is in order. At the same time, a novice user,or a less skilled user is overwhelmed by the amount of information.Also, any user intervention to the print data will inherently includeassociated cost in terms of time, device utilization and the like. It isthus desirable to have an additional method to the above-describedexpert system. This additional method will filter all problem casesbased on a relevance scheme and either resolving only these limitednumber of cases (not altering the other cases) and/or displaying onlysaid cases to a user with a simple resolution option attached.

Simple user tools will—in essentially all cases—result in a potentiallylower quality than expert tools used by expert users given sufficienttime. However, cost, available time, etc. often limit the actualmodifications an expert is capable of doing for a given job, given thoseboundary conditions. Consequently, an expert tool may be augmented by asimple intervention tool. This allows a trade-off between “perfectquality using expert intervention” and “good quality with simpleintervention”. This trade-off is often application dependent. It isimportant to note that even experts use automatic systems in cases wherethe cost of expert time would outweigh the quality benefit of expertintervention. For example, the time spent on a publication that has arun of 200,000 can be much larger than the time spent on a run of 20.Disclosed herein in embodiments is a method for color matching that canbe used by non-experts and in scenarios of short runs.

Color problems in offset transfer result predominantly from ObjectOriented Rendering (OOR) and thus can all be eliminated by avoiding OORand using SWOP emulation, i.e., switch OOR off. However, this is not agood approach, since it might lower image quality by a large amount(improved image quality is one of the main attributes of OOR). In thosecases where the cost of expert time outweighs the quality benefit ofusing the expert user methods described above, the number of objectsanalyzed can be reduced; i.e., the method filters the objects on apage-by-page bases to leave a smaller group of problem objects. Coloranalysis is then limited to those problem cases either automatically orvia display and user intervention. For purposes of this method, allpages of the print job are considered separately. Thus no comparison ismade across page boundaries, reducing the number of mismatched objectsto be displayed to a user considerably. There are generally only a fewcases where this restriction should be eliminated, but they can easilybe handled as described below.

Problem cases can easily be identified from a small number of differentparameters, such as for example, size, object type, color space andspatial proximity. Assuming a filtering process in the same order asdescribed, first eliminate all small objects inside the document fromanalysis. Small object might include all text (unless the text is wellabove normal reading font size of e.g., 12 pt), all isolated lines (notoverlapping or touching), etc. For simplicity a size less than about 1cm (0.5 inch) can be used, as the threshold for small, but it isunderstood that this can be a user configuration setting. Object sizecan be, for example, either directly calculated from the currenttransform matrix or by rendering the data in a low resolution bufferusing z-order indication, or some other methodology. Object proximitycan be calculated in the same manner. It should be understood that theforegoing filtering process may proceed based on a single parameter oron a combination of parameter efficiencies and the ease in which theparameter may be obtained from the data file. Filtering may occur in anyorder, the foregoing order being only for illustration.

A simple example can be seen in FIG. 5. In FIG. 5, a solid fillrectangle is in close proximity to several lines of small text (12 pt).All text lines have a different color and only one of the lines matchesthe color of the rectangle. For an observer, however, it is nearlyimpossible to identify the “correct” line unless slow and closeexamination is performed. From FIG. 5, it is can be seen that smallobjects do not need to be considered for an automatic color matchingmethod version (they still might be important in the expert methodsdescribed above). Filtering or eliminating small text objects from theanalysis dramatically reduces the number of objects that are maintainedfor further color matching.

In the next filtering step, the document page is filtered by object typeand color space. Here all pictorial (image data) objects are ignoredexcept those that touch graphics objects. Also, all graphics objects areeliminated if outline (stroke) and fill color are different unless theytouch other objects. An example of this is shown in FIG. 6, in whichfive smaller graphic objects having a stroke or outline are shown inproximity to, but not touching, the larger fill graphic.

In the next step, all graphics objects that have a common color spaceare eliminated (i.e., if all graphics objects on a page have theidentical color space, only objects touching other object classes arenot eliminated). For the purpose of this method, color spaces can beconsidered identical if they can uniquely be transformed into oneanother (e.g., Lab is thus equal to XYZ, but not to CMYK).

In the next step, all graphics objects that are separated by more than aspecific distance (e.g., 1 inch) are eliminated.

At this stage, only very few objects are left for examination. Touchingobjects of different object class or color space (e.g., Lab, SWOP,Pantone) remain. At least one object is of a non-image class (graphics,large text). Non-image objects of a minimum size with a minimumseparation of differing object class or color space also remain. Theseobjects may now be analyzed using the method of matching color elementsfor objects having different source color definitions and/or the methodof matching color elements for different object types having differentrendering intents described above.

The foregoing filtering process can be used to define a fully automaticcolor match tool. First all filtering is done as described above,resulting in a small number of possible conflicts. It is important tounderstand that the possible problem objects are a small subset of allobjects of the document. This in turn means that all un-marked objectscan be rendered using OOR and thus with highest possible quality. It hasto be remembered that only objects within a certain color accuracy ofeach other will be flagged, so a red square (graphics object) on a bluecircle (graphics object) will not be flagged. Also, black/white objectscan be identified as “blank space” between objects. Secondly, in fullyautomatic mode, all objects are rendered in the non-OOR mode. NormallySWOP emulation and no differing rendering intents avoid conflicts. Afully automatic system can solve the vast majority of color adjustmentproblems. At the same time, it also can be used to indicate the problemsto a “average user” by concentrating on a few visually obvious cases.

There are only a few cases, where an inter-page match is relevant for anautomatic or semi-automatic process (these cases still might be relevantin the expert mode or for specific applications). The first case is arecurring element on every page, e.g., a Company Logo. However, thiscase is easily handled. If no individual page flags the Logo as aproblem, then the Logo is simply rendered as is, since inclusion iseither by data replication or by reference and thus Logo colorconsistency is achieved automatically. If one of the pages indicates theLogo as a potential problem due to proximity with a different objectsome simple rules can be applied. In modifying one of the objects (inorder to achieve the match either rendering or color have to bemodified) always modify the un-referenced/not-reused object. The secondcase is that of a multi-page spread where different objects covermultiple pages that—after binding—appear attached. This problem issimply remedied by using a modified page definition in the analysis.Assuming that imposition is known (meaning that the page numbers are areflection of actual page order), facing pages can be re-defined to be asingle page for the purpose of the analysis and all previously describedmethods simply apply.

It should be understood that the system optionally might reverse theorder of examining color properties, object properties, etc., of thedifferent objects. If evaluating the color characteristics of an objectis computationally more costly in a given environment, a filtering basedon size, object type, etc might be performed first. If proximitycharacteristics are computationally more costly, filtering based onobject color might be performed first, etc.

The claims, as originally presented and as they may be amended,encompass variations, alternatives, modifications, improvements,equivalents, and substantial equivalents of the embodiments andteachings disclosed herein, including those that are presentlyunforeseen or unappreciated, and that, for example, may arise fromapplicants/patentees and others.

1. A computer-implemented method of matching color elements for objectswithin a print job prior to printing, comprising: for each page in theprint job, identifying all objects and their associated objectproperties within the page; for each object, identifying, according topredetermined object property criteria, if the object is a candidate fora color matching task; for each of the identified candidates, filteringthe object properties using a predetermined visual relevance metric,such that objects having less than the predetermined visual relevancemetric are removed from consideration; defining each candidate objectsatisfying the predetermined visual relevance metric as a color matchingobject with respect to at least a second color matching object thusdefining a color matching object group; and for each such color matchingobject group, either alerting a user to a problem or automaticallyresolving the problem by assigning common rendering across the colormatching object group.
 2. The method of claim 1, wherein the objectproperties include at least two of color attributes, object attributes,object location attributes and object size attributes.
 3. The method ofclaim 2, wherein at least one of the object properties comprises objectlocation such that the objects must be located within a predetermineddistance from one another.
 4. The method of claim 1, wherein thepredetermined object property criteria comprises eliminating objectssatisfying selected object properties of size, type and color space andspatial proximity.
 5. The method of claim 1, wherein the predeterminedobject property criteria comprises eliminating objects smaller than apredetermined size.
 6. The method of claim 5, wherein eliminatingobjects smaller than a predetermined size comprises eliminating all texthaving a font size 12 pt less or less, all isolated lines and allobjects having a size less than 1 cm2.
 7. The method of claim 5, furthercomprising eliminating objects of the same type having a common colorspace.
 8. The method of claim 7, wherein two objects have the same colorspace if one color space can be uniquely transformed into the othercolor space.
 9. The method of claim 7, further comprising eliminatingobjects that are separated by more than a specified distance.
 10. Acomputer-implemented method of matching color elements for objectswithin a print job prior to printing, comprising: for each page in theprint job, identifying all objects and their associated objectproperties within the page; for each object, identifying, according topredetermined object property criteria, if the object is a candidate fora color matching task; for each of the identified candidates, filteringthe object properties using a predetermined visual relevance metric,such that objects having less than the predetermined visual relevancemetric are removed from consideration; defining each candidate objectsatisfying the predetermined visual relevance metric as a color matchingobject with respect to at least a second color matching object thusdefining a color matching object group; and for each such color matchingobject group, automatically resolving any color mismatch by assigningcommon rendering across the color matching object group.
 11. The methodof claim 10, wherein the object properties include at least two of colorattributes, object attributes, object location attributes and objectsize attributes.
 12. The method of claim 10, further comprisingrendering all objects not in a color matching object group according totheir originally assigned rendering technique.
 13. The method of claim10, further comprising: identifying any objects occurring on multiplepages; assigning the same rendering technique to such objects.
 14. Themethod of claim 10, further comprising prior to identifying all objectsand their associated object properties within a page, defining facingpages as a single page.
 15. The method of claim 10, wherein thepredetermined object properties include at least two of colorattributes, object attributes, object location attributes and objectsize attributes and wherein identifying, according to predeterminedobject property criteria, comprises examining color properties prior toexamining object attributes, object location attributes and object sizeattributes.
 16. The method of claim 10, wherein the predetermined objectproperties include at least two of color attributes, object attributes,object location attributes and object size attributes and whereinidentifying, according to predetermined object property criteria,comprises examining color properties after examining object attributes,object location attributes and object size attributes.